The present invention relates to an electron source using a plurality of surfaceconduction electron-emitting devices, an image forming apparatus such as a display apparatus or an exposure apparatus using the electron source, and a method of manufacturing and adjusting the electron source.
Two types of electron sources, namely thermionic sources and cold cathode electron sources, are conventionally known as electron-emitting devices. Examples of cold cathode electron sources are electron-emitting devices of the field emission type (to be abbreviated to "FE" hereinafter), metal/insulator/metal type (to be abbreviated to "MIM" hereinafter), and surfaceconduction emission type.
Known examples of the FE type are described by W. P. Dyke and W. W. Dolan, "Field emission", Advance in Electron Physics, 8,89 (1956) and by C. A. Spindt, "Physical properties of thin-film field emission cathodes with molybdenum cones", J. Appl. Phys., 47,5248 (1976).
A known example of the MIM type is described by C. A. Mead, "Operation of Tunnel-Emission Devices", J. Appl. Phys., 32,646 (1961).
A known example of the surfaceconduction electron-emitting device is described by M. I. Elinson, Radio. Eng. Electron Phys., 10 (1965).
The surfaceconduction electron-emitting device makes use of a phenomenon in which electron emission is produced in a thin conductive film formed on an insulating substrate by passing a current parallel to the film surface. Various examples of this surfaceconduction electron-emitting device have been reported. One relies upon a thin film of SnO.sub.2 according to Elinson, mentioned above. Other examples use a thin film of Au [G. Dittmer, "Thin Solid Films", 9,317 (1972)]; a thin film of In.sub.2 O.sub.3 /SnO.sub.2 [M. Hartwell and C. G. Fonstad, "IEEE Trans. E.D. Conf.", 519 (1975)]; and a thin film of carbon [Hisashi Araki, et al: "Vacuum", Vol. 26, No. 1, p. 22 (1983)].
A typical construction example of the surfaceconduction electron-emitting device is of the type according to M. Hartwell above, in which an electron emission portion is formed by an electrification process called "energization forming" on a thin conductive film of a metal oxide or the like, which formed between a pair of device electrodes on an insulating substrate. A spacing between the device electrodes of the surfaceconduction electron-emitting device is set to 0.5 to 1 mm. The width of the device electrode is set to 0.1 mm.
In these surfaceconduction electron-emitting devices, generally, the electron emission portion is formed on the thin conductive film by the electrification process called "energization forming" before electron emission is performed. According to this energization forming process, a DC voltage or a very slowly rising voltage on the order of, e.g., 1 V/min is impressed across the thin conductive film, thereby locally destroying or deforming the thin conductive film, or changing its properties to change the construction. With this process, the electron emission portion having a high electrical resistance is formed. When a voltage is applied to the thin conductive film to form the electron emission portion, fissures are formed in the conductive film, and electrons are emitted from the vicinity of the fissures.
Since the surfaceconduction electron-emitting device is simple in structure and easy to manufacture, an advantage is that a large number of devices can be arrayed over a large surface area. Accordingly, a variety of applications that exploit this feature have been studied. For example, an application to an image forming apparatus such as a display apparatus has been made.
As a conventional example of an apparatus in which a number of surfaceconduction electron-emitting devices are formed on an array, mention can be made of an electron source in which surfaceconduction electron-emitting devices are arrayed in parallel, and both ends (double device electrodes) of the individual devices are connected by a wiring layer (also referred to as a common wiring layer) to obtain a row, a number of which are provided in an array (also referred to as a "ladder-shaped" array), (Japanese Patent Laid-Open Nos. 1-31332, 1-283749, and 1-257552). Particularly, for a display apparatus, a flat-type display apparatus which emits its own light without requiring backlighting has been proposed, which comprises a combination of an electron source having a large number of surfaceconduction electron-emitting devices and phosphors that produce visible light from the electron source upon irradiation of an electron beam (U.S. Pat. No. 5,066,883).
However, the conventional electron source using the surfaceconduction electron-emitting devices has the following problems.
When a large number of surfaceconduction electron-emitting devices are to be formed on a substrate, the shape or material composition may vary in units of devices, resulting in non-uniform electron emission characteristics of the manufactured devices.
For example, when the deposition conditions or patterning conditions in a process of forming an electrode or a thin conductive film vary, the characteristics of the manufactured devices may vary in units of substrates. Even in the same substrate, the characteristics may change in units of devices.
Similarly, when electrification conditions in the energization forming process vary in units of devices, the electron emission characteristics may change.
A distribution tends to be formed in the energization forming voltage due to the variation in resistance of the thin film, or a voltage drop caused by the resistance of wiring for connecting a large number of surfaceconduction electron-emitting devices, so the surfaceconduction electron-emitting devices can hardly be subjected to the energization forming process under the same conditions. The resistance values or electron emission characteristics of the surfaceconduction electron-emitting devices after energization forming vary accordingly. When the applied voltage-to-emission current characteristics vary, the emission electron amount (or the light emission luminance in a display apparatus) varies in units of surfaceconduction electron-emitting devices, resulting in a luminance variation of the display apparatus.
As described above, the electron emission characteristics of the surfaceconduction electron-emitting device often vary due to various factors generated in the film-forming process, the patterning process, the energization forming process, or the electrification activation process of the manufacturing processes of the electron source. Conventionally, if the electron emission characteristics of a manufactured surfaceconduction electron-emitting device vary beyond the required allowance for the application purpose, the electron source is discarded as a defective product, or a driving correction circuit for correcting the variation in characteristics is added to make use of the electron source. The former lowers the manufacturing yield rate to result in an increase in cost, and the latter results in an increase in cost and a bulky apparatus because of the additional correction circuit.
Therefore, in the electron source using a plurality of surfaceconduction electron-emitting devices, the electrical characteristics of the respective surfaceconduction electron-emitting devices are required to be uniform and easy to control.